The current mechanical stretching device of sofa has four major disadvantages: 1, in the market, the adjustable sofa pauses obviously when opened, influencing the comfortability of running of the sofa; 2, in the market, the opening limit device of the adjustable sofa will give rise to two hitting sounds, influencing the comfortability of the adjustable sofa; 3, in the market, in the electrically driving process of the adjustable sofa, the mechanical stretching device is opened in the swing process and the limit will be jammed so that the mechanical stretching device is damaged and even hurts users with serious potential safety hazard; and 4, in the market, the adjustable sofa opens the mechanical stretching device in the swing process so that there will be obvious shaking phenomenon, influencing the function and structural stability of the sofa. Referring to FIG. 7 and FIG. 8, in the market, the mechanical stretching device of adjustable sofa in the prior art comprises a hook connector 39, a limit drive connector 43, a contrast leg drive connector 44 (the “contrast” herein is used to be distinguished from the embodiment, similarly hereinafter), a contrast back swing connector 42, a contrast transmission connector 40, and a back swing connector limit 41. The back swing connector limit 41 is fixedly connected on the contrast back swing connector 42; the hook connector 39 is rotatably connected to the contrast transmission connector 40 via a first axis of rotation 45, rotatably connected to the limit drive connector 43 via a second axis of rotation 46, and rotatably connected to the contrast leg drive connector 44 via a third axis of rotation 47. When the contrast back swing connector 42 swings to a position in the opening process of the mechanical stretching device, the mechanical stretching device can be completely opened so as to give rise to the second pause only after the back swing connector limit 41 touches the limit groove on the hook connector 39 so as to give rise to the first pause. At this time, there will be obvious shaking phenomenon in the mechanical stretching device of adjustable sofa.